PERLVMS(1) Perl Programmers Reference Guide PERLVMS(1)
NAME
perlvms - VMS-specific documentation for Perl
DESCRIPTION
Gathered below are notes describing details of Perl 5's behavior on VMS. They are a supplement to the regular
Perl 5 documentation, so we have focussed on the ways in which Perl 5 functions differently under VMS than it
does under Unix, and on the interactions between Perl and the rest of the operating system. We haven't tried
to duplicate complete descriptions of Perl features from the main Perl documentation, which can be found in
the [.pod] subdirectory of the Perl distribution.
We hope these notes will save you from confusion and lost sleep when writing Perl scripts on VMS. If you find
we've missed something you think should appear here, please don't hesitate to drop a line to [email protected].
Installation
Directions for building and installing Perl 5 can be found in the file README.vms in the main source directory
of the Perl distribution..
Organization of Perl Images
Core Images
During the installation process, three Perl images are produced. Miniperl.Exe is an executable image which
contains all of the basic functionality of Perl, but cannot take advantage of Perl extensions. It is used to
generate several files needed to build the complete Perl and various extensions. Once you've finished
installing Perl, you can delete this image.
Most of the complete Perl resides in the shareable image PerlShr.Exe, which provides a core to which the Perl
executable image and all Perl extensions are linked. You should place this image in Sys$Share, or define the
logical name PerlShr to translate to the full file specification of this image. It should be world readable.
(Remember that if a user has execute only access to PerlShr, VMS will treat it as if it were a privileged
shareable image, and will therefore require all downstream shareable images to be INSTALLed, etc.)
Finally, Perl.Exe is an executable image containing the main entry point for Perl, as well as some
initialization code. It should be placed in a public directory, and made world executable. In order to run
Perl with command line arguments, you should define a foreign command to invoke this image.
Perl Extensions
Perl extensions are packages which provide both XS and Perl code to add new functionality to perl. (XS is a
meta-language which simplifies writing C code which interacts with Perl, see perlxs for more details.) The
Perl code for an extension is treated like any other library module - it's made available in your script
through the appropriate "use" or "require" statement, and usually defines a Perl package containing the
extension.
The portion of the extension provided by the XS code may be connected to the rest of Perl in either of two
ways. In the static configuration, the object code for the extension is linked directly into PerlShr.Exe, and
is initialized whenever Perl is invoked. In the dynamic configuration, the extension's machine code is placed
into a separate shareable image, which is mapped by Perl's DynaLoader when the extension is "use"d or
"require"d in your script. This allows you to maintain the extension as a separate entity, at the cost of
keeping track of the additional shareable image. Most extensions can be set up as either static or dynamic.
The source code for an extension usually resides in its own directory. At least three files are generally
provided: Extshortname.xs (where Extshortname is the portion of the extension's name following the last "::"),
containing the XS code, Extshortname.pm, the Perl library module for the extension, and Makefile.PL, a Perl
script which uses the "MakeMaker" library modules supplied with Perl to generate a Descrip.MMS file for the
extension.
Installing static extensions
Since static extensions are incorporated directly into PerlShr.Exe, you'll have to rebuild Perl to incorporate
by the extension. The kit should be unpacked into a directory tree not under the main Perl source directory,
and the procedure for building the extension is simply
$ perl Makefile.PL ! Create Descrip.MMS
$ mmk ! Build necessary files
$ mmk test ! Run test code, if supplied
$ mmk install ! Install into public Perl tree
N.B. The procedure by which extensions are built and tested creates several levels (at least 4) under the
directory in which the extension's source files live. For this reason if you are running a version of VMS
prior to V7.1 you shouldn't nest the source directory too deeply in your directory structure lest you exceed
RMS' maximum of 8 levels of subdirectory in a filespec. (You can use rooted logical names to get another 8
levels of nesting, if you can't place the files near the top of the physical directory structure.)
VMS support for this process in the current release of Perl is sufficient to handle most extensions. However,
it does not yet recognize extra libraries required to build shareable images which are part of an extension,
so these must be added to the linker options file for the extension by hand. For instance, if the PGPLOT
extension to Perl requires the PGPLOTSHR.EXE shareable image in order to properly link the Perl extension,
then the line "PGPLOTSHR/Share" must be added to the linker options file PGPLOT.Opt produced during the build
process for the Perl extension.
By default, the shareable image for an extension is placed in the [.lib.site_perl.autoArch.Extname] directory
of the installed Perl directory tree (where Arch is VMS_VAX or VMS_AXP, and Extname is the name of the
extension, with each "::" translated to "."). (See the MakeMaker documentation for more details on
installation options for extensions.) However, it can be manually placed in any of several locations:
· the [.Lib.Auto.Arch$PVersExtname] subdirectory of one of the directories in @INC (where PVers is the
version of Perl you're using, as supplied in $], with '.' converted to '_'), or
· one of the directories in @INC, or
· a directory which the extensions Perl library module passes to the DynaLoader when asking it to map the
shareable image, or
· Sys$Share or Sys$Library.
If the shareable image isn't in any of these places, you'll need to define a logical name Extshortname, where
Extshortname is the portion of the extension's name after the last "::", which translates to the full file
specification of the shareable image.
File specifications
Syntax
We have tried to make Perl aware of both VMS-style and Unix-style file specifications wherever possible. You
may use either style, or both, on the command line and in scripts, but you may not combine the two styles
within a single file specification. VMS Perl interprets Unix pathnames in much the same way as the CRTL (e.g.
the first component of an absolute path is read as the device name for the VMS file specification). There are
a set of functions provided in the "VMS::Filespec" package for explicit interconversion between VMS and Unix
syntax; its documentation provides more details.
We've tried to minimize the dependence of Perl library modules on Unix syntax, but you may find that some of
these, as well as some scripts written for Unix systems, will require that you use Unix syntax, since they
will assume that '/' is the directory separator, etc. If you find instances of this in the Perl distribution
itself, please let us know, so we can try to work around them.
work is still needed to fully support extended syntax filenames in several core modules. In particular, at
this writing PathTools has only partial support for directories containing some extended characters.
There are several ambiguous cases where a conversion routine cannot determine whether an input filename is in
Unix format or in VMS format, since now both VMS and Unix file specifications may have characters in them that
could be mistaken for syntax delimiters of the other type. So some pathnames simply cannot be used in a mode
that allows either type of pathname to be present. Perl will tend to assume that an ambiguous filename is in
Unix format.
Allowing "." as a version delimiter is simply incompatible with determining whether a pathname is in VMS
format or in Unix format with extended file syntax. There is no way to know whether "perl-5.8.6" is a Unix
"perl-5.8.6" or a VMS "perl-5.8;6" when passing it to unixify() or vmsify().
The DECC$FILENAME_UNIX_REPORT logical name controls how Perl interprets filenames to the extent that Perl uses
the CRTL internally for many purposes, and attempts to follow CRTL conventions for reporting filenames. The
DECC$FILENAME_UNIX_ONLY feature differs in that it expects all filenames passed to the C run-time to be
already in Unix format. This feature is not yet supported in Perl since Perl uses traditional OpenVMS file
specifications internally and in the test harness, and it is not yet clear whether this mode will be useful or
useable. The feature logical name DECC$POSIX_COMPLIANT_PATHNAMES is new with the RMS Symbolic Link SDK and
included with OpenVMS v8.3, but is not yet supported in Perl.
Filename Case
Perl follows VMS defaults and override settings in preserving (or not preserving) filename case. Case is not
preserved on ODS-2 formatted volumes on any architecture. On ODS-5 volumes, filenames may be case preserved
depending on process and feature settings. Perl now honors DECC$EFS_CASE_PRESERVE and DECC$ARGV_PARSE_STYLE
on those systems where the CRTL supports these features. When these features are not enabled or the CRTL does
not support them, Perl follows the traditional CRTL behavior of downcasing command-line arguments and
returning file specifications in lower case only.
N. B. It is very easy to get tripped up using a mixture of other programs, external utilities, and Perl
scripts that are in varying states of being able to handle case preservation. For example, a file created by
an older version of an archive utility or a build utility such as MMK or MMS may generate a filename in all
upper case even on an ODS-5 volume. If this filename is later retrieved by a Perl script or module in a case
preserving environment, that upper case name may not match the mixed-case or lower-case exceptions of the Perl
code. Your best bet is to follow an all-or-nothing approach to case preservation: either don't use it at all,
or make sure your entire toolchain and application environment support and use it.
OpenVMS Alpha v7.3-1 and later and all version of OpenVMS I64 support case sensitivity as a process setting
(see "SET PROCESS /CASE_LOOKUP=SENSITIVE"). Perl does not currently support case sensitivity on VMS, but it
may in the future, so Perl programs should use the "File::Spec->case_tolerant" method to determine the state,
and not the $^O variable.
Symbolic Links
When built on an ODS-5 volume with symbolic links enabled, Perl by default supports symbolic links when the
requisite support is available in the filesystem and CRTL (generally 64-bit OpenVMS v8.3 and later). There
are a number of limitations and caveats to be aware of when working with symbolic links on VMS. Most notably,
the target of a valid symbolic link must be expressed as a Unix-style path and it must exist on a volume
visible from your POSIX root (see the "SHOW ROOT" command in DCL help). For further details on symbolic link
capabilities and requirements, see chapter 12 of the CRTL manual that ships with OpenVMS v8.3 or later.
Wildcard expansion
File specifications containing wildcards are allowed both on the command line and within Perl globs (e.g.
"<*.c>"). If the wildcard filespec uses VMS syntax, the resultant filespecs will follow VMS syntax; if a
Unix-style filespec is passed in, Unix-style filespecs will be returned. Similar to the behavior of wildcard
In both the case of unquoted command line arguments or in calls to "glob()" VMS wildcard expansion is
performed. (csh-style wildcard expansion is available if you use "File::Glob::glob".) If the wildcard
filespec contains a device or directory specification, then the resultant filespecs will also contain a device
and directory; otherwise, device and directory information are removed. VMS-style resultant filespecs will
contain a full device and directory, while Unix-style resultant filespecs will contain only as much of a
directory path as was present in the input filespec. For example, if your default directory is
Perl_Root:[000000], the expansion of "[.t]*.*" will yield filespecs like "perl_root:[t]base.dir", while the
expansion of "t/*/*" will yield filespecs like "t/base.dir". (This is done to match the behavior of glob
expansion performed by Unix shells.)
Similarly, the resultant filespec will contain the file version only if one was present in the input filespec.
Pipes
Input and output pipes to Perl filehandles are supported; the "file name" is passed to lib$spawn() for
asynchronous execution. You should be careful to close any pipes you have opened in a Perl script, lest you
leave any "orphaned" subprocesses around when Perl exits.
You may also use backticks to invoke a DCL subprocess, whose output is used as the return value of the
expression. The string between the backticks is handled as if it were the argument to the "system" operator
(see below). In this case, Perl will wait for the subprocess to complete before continuing.
The mailbox (MBX) that perl can create to communicate with a pipe defaults to a buffer size of 8192 on 64-bit
systems, 512 on VAX. The default buffer size is adjustable via the logical name PERL_MBX_SIZE provided that
the value falls between 128 and the SYSGEN parameter MAXBUF inclusive. For example, to set the mailbox size
to 32767 use "$ENV{'PERL_MBX_SIZE'} = 32767;" and then open and use pipe constructs. An alternative would be
to issue the command:
$ Define PERL_MBX_SIZE 32767
before running your wide record pipe program. A larger value may improve performance at the expense of the
BYTLM UAF quota.
PERL5LIB and PERLLIB
The PERL5LIB and PERLLIB logical names work as documented in perl, except that the element separator is '|'
instead of ':'. The directory specifications may use either VMS or Unix syntax.
The Perl Forked Debugger
The Perl forked debugger places the debugger commands and output in a separate X-11 terminal window so that
commands and output from multiple processes are not mixed together.
Perl on VMS supports an emulation of the forked debugger when Perl is run on a VMS system that has X11 support
installed.
To use the forked debugger, you need to have the default display set to an X-11 Server and some environment
variables set that Unix expects.
The forked debugger requires the environment variable "TERM" to be "xterm", and the environment variable
"DISPLAY" to exist. "xterm" must be in lower case.
$define TERM "xterm"
$define DISPLAY "hostname:0.0"
exception that is not otherwise handled is raised. The purpose of this is to allow debugging of internal Perl
problems that would cause such a condition.
This allows the programmer to look at the execution stack and variables to find out the cause of the
exception. As the debugger is being invoked as the Perl interpreter is about to do a fatal exit, continuing
the execution in debug mode is usually not practical.
Starting Perl in the VMS debugger may change the program execution profile in a way that such problems are not
reproduced.
The "kill" function can be used to test this functionality from within a program.
In typical VMS style, only the first letter of the value of this logical name is actually checked in a case
insensitive mode, and it is considered enabled if it is the value "T","1" or "E".
This logical name must be defined before Perl is started.
Command line
I/O redirection and backgrounding
Perl for VMS supports redirection of input and output on the command line, using a subset of Bourne shell
syntax:
· "<file" reads stdin from "file",
· ">file" writes stdout to "file",
· ">>file" appends stdout to "file",
· "2>file" writes stderr to "file",
· "2>>file" appends stderr to "file", and
· "2>&1" redirects stderr to stdout.
In addition, output may be piped to a subprocess, using the character '|'. Anything after this character on
the command line is passed to a subprocess for execution; the subprocess takes the output of Perl as its
input.
Finally, if the command line ends with '&', the entire command is run in the background as an asynchronous
subprocess.
Command line switches
The following command line switches behave differently under VMS than described in perlrun. Note also that in
order to pass uppercase switches to Perl, you need to enclose them in double-quotes on the command line, since
the CRTL downcases all unquoted strings.
On newer 64 bit versions of OpenVMS, a process setting now controls if the quoting is needed to preserve the
case of command line arguments.
-i If the "-i" switch is present but no extension for a backup copy is given, then inplace editing creates a
new version of a file; the existing copy is not deleted. (Note that if an extension is given, an existing
file is renamed to the backup file, as is the case under other operating systems, so it does not remain as
a previous version under the original filename.)
file tests*, abs, alarm, atan, backticks*, binmode*, bless,
caller, chdir, chmod, chown, chomp, chop, chr,
close, closedir, cos, crypt*, defined, delete, die, do, dump*,
each, endgrent, endpwent, eof, eval, exec*, exists, exit, exp,
fileno, flock getc, getgrent*, getgrgid*, getgrnam, getlogin, getppid,
getpwent*, getpwnam*, getpwuid*, glob, gmtime*, goto,
grep, hex, ioctl, import, index, int, join, keys, kill*,
last, lc, lcfirst, lchown*, length, link*, local, localtime, log, lstat, m//,
map, mkdir, my, next, no, oct, open, opendir, ord, pack,
pipe, pop, pos, print, printf, push, q//, qq//, qw//,
qx//*, quotemeta, rand, read, readdir, readlink*, redo, ref, rename,
require, reset, return, reverse, rewinddir, rindex,
rmdir, s///, scalar, seek, seekdir, select(internal),
select (system call)*, setgrent, setpwent, shift, sin, sleep,
socketpair, sort, splice, split, sprintf, sqrt, srand, stat,
study, substr, symlink*, sysread, system*, syswrite, tell,
telldir, tie, time, times*, tr///, uc, ucfirst, umask,
undef, unlink*, unpack, untie, unshift, use, utime*,
values, vec, wait, waitpid*, wantarray, warn, write, y///
The following functions were not implemented in the VMS port, and calling them produces a fatal error
(usually) or undefined behavior (rarely, we hope):
chroot, dbmclose, dbmopen, fork*, getpgrp, getpriority,
msgctl, msgget, msgsend, msgrcv, semctl,
semget, semop, setpgrp, setpriority, shmctl, shmget,
shmread, shmwrite, syscall
The following functions are available on Perls compiled with Dec C 5.2 or greater and running VMS 7.0 or
greater:
truncate
The following functions are available on Perls built on VMS 7.2 or greater:
fcntl (without locking)
The following functions may or may not be implemented, depending on what type of socket support you've built
into your copy of Perl:
accept, bind, connect, getpeername,
gethostbyname, getnetbyname, getprotobyname,
getservbyname, gethostbyaddr, getnetbyaddr,
getprotobynumber, getservbyport, gethostent,
getnetent, getprotoent, getservent, sethostent,
setnetent, setprotoent, setservent, endhostent,
endnetent, endprotoent, endservent, getsockname,
getsockopt, listen, recv, select(system call)*,
send, setsockopt, shutdown, socket
The following function is available on Perls built on 64 bit OpenVMS v8.2 with hard links enabled on an ODS-5
formatted build disk. CRTL support is in principle available as of OpenVMS v7.3-1, and better configuration
support could detect this.
File tests
The tests "-b", "-B", "-c", "-C", "-d", "-e", "-f", "-o", "-M", "-s", "-S", "-t", "-T", and "-z" work as
advertised. The return values for "-r", "-w", and "-x" tell you whether you can actually access the file;
this may not reflect the UIC-based file protections. Since real and effective UIC don't differ under VMS,
"-O", "-R", "-W", and "-X" are equivalent to "-o", "-r", "-w", and "-x". Similarly, several other tests,
including "-A", "-g", "-k", "-l", "-p", and "-u", aren't particularly meaningful under VMS, and the values
returned by these tests reflect whatever your CRTL "stat()" routine does to the equivalent bits in the
st_mode field. Finally, "-d" returns true if passed a device specification without an explicit directory
(e.g. "DUA1:"), as well as if passed a directory.
There are DECC feature logical names AND ODS-5 volume attributes that also control what values are
returned for the date fields.
Note: Some sites have reported problems when using the file-access tests ("-r", "-w", and "-x") on files
accessed via DEC's DFS. Specifically, since DFS does not currently provide access to the extended file
header of files on remote volumes, attempts to examine the ACL fail, and the file tests will return false,
with $! indicating that the file does not exist. You can use "stat" on these files, since that checks
UIC-based protection only, and then manually check the appropriate bits, as defined by your C compiler's
stat.h, in the mode value it returns, if you need an approximation of the file's protections.
backticks
Backticks create a subprocess, and pass the enclosed string to it for execution as a DCL command. Since
the subprocess is created directly via "lib$spawn()", any valid DCL command string may be specified.
binmode FILEHANDLE
The "binmode" operator will attempt to insure that no translation of carriage control occurs on input from
or output to this filehandle. Since this involves reopening the file and then restoring its file position
indicator, if this function returns FALSE, the underlying filehandle may no longer point to an open file,
or may point to a different position in the file than before "binmode" was called.
Note that "binmode" is generally not necessary when using normal filehandles; it is provided so that you
can control I/O to existing record-structured files when necessary. You can also use the "vmsfopen"
function in the VMS::Stdio extension to gain finer control of I/O to files and devices with different
record structures.
crypt PLAINTEXT, USER
The "crypt" operator uses the "sys$hash_password" system service to generate the hashed representation of
PLAINTEXT. If USER is a valid username, the algorithm and salt values are taken from that user's UAF
record. If it is not, then the preferred algorithm and a salt of 0 are used. The quadword encrypted
value is returned as an 8-character string.
The value returned by "crypt" may be compared against the encrypted password from the UAF returned by the
"getpw*" functions, in order to authenticate users. If you're going to do this, remember that the
encrypted password in the UAF was generated using uppercase username and password strings; you'll have to
upcase the arguments to "crypt" to insure that you'll get the proper value:
sub validate_passwd {
my($user,$passwd) = @_;
my($pwdhash);
if ( !($pwdhash = (getpwnam($user))[1]) ||
$pwdhash ne crypt("\U$passwd","\U$name") ) {
intruder_alert($name);
}
return 1;
apply, the Unix value of 255 will be encoded into a native VMS exit status value.
Please note a significant difference in the behavior of "die" in the "PERL_VMS_POSIX_EXIT" mode is that it
does not force a VMS SEVERE_ERROR status on exit. The Unix exit values of 2 through 255 will be encoded
in VMS status values with severity levels of SUCCESS. The Unix exit value of 1 will be encoded in a VMS
status value with a severity level of ERROR. This is to be compatible with how the VMS C library encodes
these values.
The minimum severity level set by "die" in "PERL_VMS_POSIX_EXIT" mode may be changed to be ERROR or higher
in the future depending on the results of testing and further review.
See "$?" for a description of the encoding of the Unix value to produce a native VMS status containing it.
dump
Rather than causing Perl to abort and dump core, the "dump" operator invokes the VMS debugger. If you
continue to execute the Perl program under the debugger, control will be transferred to the label
specified as the argument to "dump", or, if no label was specified, back to the beginning of the program.
All other state of the program (e.g. values of variables, open file handles) are not affected by calling
"dump".
exec LIST
A call to "exec" will cause Perl to exit, and to invoke the command given as an argument to "exec" via
"lib$do_command". If the argument begins with '@' or '$' (other than as part of a filespec), then it is
executed as a DCL command. Otherwise, the first token on the command line is treated as the filespec of
an image to run, and an attempt is made to invoke it (using .Exe and the process defaults to expand the
filespec) and pass the rest of "exec"'s argument to it as parameters. If the token has no file type, and
matches a file with null type, then an attempt is made to determine whether the file is an executable
image which should be invoked using "MCR" or a text file which should be passed to DCL as a command
procedure.
fork
While in principle the "fork" operator could be implemented via (and with the same rather severe
limitations as) the CRTL "vfork()" routine, and while some internal support to do just that is in place,
the implementation has never been completed, making "fork" currently unavailable. A true kernel "fork()"
is expected in a future version of VMS, and the pseudo-fork based on interpreter threads may be available
in a future version of Perl on VMS (see perlfork). In the meantime, use "system", backticks, or piped
filehandles to create subprocesses.
getpwent
getpwnam
getpwuid
These operators obtain the information described in perlfunc, if you have the privileges necessary to
retrieve the named user's UAF information via "sys$getuai". If not, then only the $name, $uid, and $gid
items are returned. The $dir item contains the login directory in VMS syntax, while the $comment item
contains the login directory in Unix syntax. The $gcos item contains the owner field from the UAF record.
The $quota item is not used.
gmtime
The "gmtime" operator will function properly if you have a working CRTL "gmtime()" routine, or if the
logical name SYS$TIMEZONE_DIFFERENTIAL is defined as the number of seconds which must be added to UTC to
yield local time. (This logical name is defined automatically if you are running a version of VMS with
built-in UTC support.) If neither of these cases is true, a warning message is printed, and "undef" is
returned.
See the entry on "backticks" above.
select (system call)
If Perl was not built with socket support, the system call version of "select" is not available at all.
If socket support is present, then the system call version of "select" functions only for file descriptors
attached to sockets. It will not provide information about regular files or pipes, since the CRTL
"select()" routine does not provide this functionality.
stat EXPR
Since VMS keeps track of files according to a different scheme than Unix, it's not really possible to
represent the file's ID in the "st_dev" and "st_ino" fields of a "struct stat". Perl tries its best,
though, and the values it uses are pretty unlikely to be the same for two different files. We can't
guarantee this, though, so caveat scriptor.
system LIST
The "system" operator creates a subprocess, and passes its arguments to the subprocess for execution as a
DCL command. Since the subprocess is created directly via "lib$spawn()", any valid DCL command string may
be specified. If the string begins with '@', it is treated as a DCL command unconditionally. Otherwise,
if the first token contains a character used as a delimiter in file specification (e.g. ":" or "]"), an
attempt is made to expand it using a default type of .Exe and the process defaults, and if successful,
the resulting file is invoked via "MCR". This allows you to invoke an image directly simply by passing the
file specification to "system", a common Unixish idiom. If the token has no file type, and matches a file
with null type, then an attempt is made to determine whether the file is an executable image which should
be invoked using "MCR" or a text file which should be passed to DCL as a command procedure.
If LIST consists of the empty string, "system" spawns an interactive DCL subprocess, in the same fashion
as typing SPAWN at the DCL prompt.
Perl waits for the subprocess to complete before continuing execution in the current process. As
described in perlfunc, the return value of "system" is a fake "status" which follows POSIX semantics
unless the pragma "use vmsish 'status'" is in effect; see the description of $? in this document for more
detail.
time
The value returned by "time" is the offset in seconds from 01-JAN-1970 00:00:00 (just like the CRTL's
times() routine), in order to make life easier for code coming in from the POSIX/Unix world.
times
The array returned by the "times" operator is divided up according to the same rules the CRTL "times()"
routine. Therefore, the "system time" elements will always be 0, since there is no difference between
"user time" and "system" time under VMS, and the time accumulated by a subprocess may or may not appear
separately in the "child time" field, depending on whether "times()" keeps track of subprocesses
separately. Note especially that the VAXCRTL (at least) keeps track only of subprocesses spawned using
"fork()" and "exec()"; it will not accumulate the times of subprocesses spawned via pipes, "system()", or
backticks.
unlink LIST
"unlink" will delete the highest version of a file only; in order to delete all versions, you need to say
1 while unlink LIST;
You may need to make this change to scripts written for a Unix system which expect that after a call to
"unlink", no files with the names passed to "unlink" will exist. (Note: This can be changed at compile
time; if you "use Config" and $Config{'d_unlink_all_versions'} is "define", then "unlink" will delete all
}
$num;
}
(or you could just use "VMS::Stdio::remove", if you've installed the VMS::Stdio extension distributed with
Perl). If "unlink" has to change the file protection to delete the file, and you interrupt it in
midstream, the file may be left intact, but with a changed ACL allowing you delete access.
This behavior of "unlink" is to be compatible with POSIX behavior and not traditional VMS behavior.
utime LIST
This operator changes only the modification time of the file (VMS revision date) on ODS-2 volumes and
ODS-5 volumes without access dates enabled. On ODS-5 volumes with access dates enabled, the true access
time is modified.
waitpid PID,FLAGS
If PID is a subprocess started by a piped "open()" (see open), "waitpid" will wait for that subprocess,
and return its final status value in $?. If PID is a subprocess created in some other way (e.g. SPAWNed
before Perl was invoked), "waitpid" will simply check once per second whether the process has completed,
and return when it has. (If PID specifies a process that isn't a subprocess of the current process, and
you invoked Perl with the "-w" switch, a warning will be issued.)
Returns PID on success, -1 on error. The FLAGS argument is ignored in all cases.
Perl variables
The following VMS-specific information applies to the indicated "special" Perl variables, in addition to the
general information in perlvar. Where there is a conflict, this information takes precedence.
%ENV
The operation of the %ENV array depends on the translation of the logical name PERL_ENV_TABLES. If
defined, it should be a search list, each element of which specifies a location for %ENV elements. If you
tell Perl to read or set the element "$ENV{"name"}", then Perl uses the translations of PERL_ENV_TABLES as
follows:
CRTL_ENV
This string tells Perl to consult the CRTL's internal "environ" array of key-value pairs, using name
as the key. In most cases, this contains only a few keys, but if Perl was invoked via the C
"exec[lv]e()" function, as is the case for CGI processing by some HTTP servers, then the "environ"
array may have been populated by the calling program.
CLISYM_[LOCAL]
A string beginning with "CLISYM_"tells Perl to consult the CLI's symbol tables, using name as the name
of the symbol. When reading an element of %ENV, the local symbol table is scanned first, followed by
the global symbol table.. The characters following "CLISYM_" are significant when an element of %ENV
is set or deleted: if the complete string is "CLISYM_LOCAL", the change is made in the local symbol
table; otherwise the global symbol table is changed.
Any other string
If an element of PERL_ENV_TABLES translates to any other string, that string is used as the name of a
logical name table, which is consulted using name as the logical name. The normal search order of
access modes is used.
PERL_ENV_TABLES is translated once when Perl starts up; any changes you make while Perl is running do not
affect the behavior of %ENV. If PERL_ENV_TABLES is not defined, then Perl defaults to consulting first
$ Define STORY once,upon,a,time,there,was
$ perl -e "for ($i = 0; $i <= 6; $i++) " -
_$ -e "{ print $ENV{'story;'.$i},' '}"
Perl will print "ONCE UPON A TIME THERE WAS", assuming, of course, that PERL_ENV_TABLES is set up so that
the logical name "story" is found, rather than a CLI symbol or CRTL "environ" element with the same name.
When an element of %ENV is set to a defined string, the corresponding definition is made in the location
to which the first translation of PERL_ENV_TABLES points. If this causes a logical name to be created, it
is defined in supervisor mode. (The same is done if an existing logical name was defined in executive or
kernel mode; an existing user or supervisor mode logical name is reset to the new value.) If the value is
an empty string, the logical name's translation is defined as a single NUL (ASCII 00) character, since a
logical name cannot translate to a zero-length string. (This restriction does not apply to CLI symbols or
CRTL "environ" values; they are set to the empty string.) An element of the CRTL "environ" array can be
set only if your copy of Perl knows about the CRTL's "setenv()" function. (This is present only in some
versions of the DECCRTL; check $Config{d_setenv} to see whether your copy of Perl was built with a CRTL
that has this function.)
When an element of %ENV is set to "undef", the element is looked up as if it were being read, and if it is
found, it is deleted. (An item "deleted" from the CRTL "environ" array is set to the empty string; this
can only be done if your copy of Perl knows about the CRTL "setenv()" function.) Using "delete" to remove
an element from %ENV has a similar effect, but after the element is deleted, another attempt is made to
look up the element, so an inner-mode logical name or a name in another location will replace the logical
name just deleted. In either case, only the first value found searching PERL_ENV_TABLES is altered. It
is not possible at present to define a search list logical name via %ENV.
The element $ENV{DEFAULT} is special: when read, it returns Perl's current default device and directory,
and when set, it resets them, regardless of the definition of PERL_ENV_TABLES. It cannot be cleared or
deleted; attempts to do so are silently ignored.
Note that if you want to pass on any elements of the C-local environ array to a subprocess which isn't
started by fork/exec, or isn't running a C program, you can "promote" them to logical names in the current
process, which will then be inherited by all subprocesses, by saying
foreach my $key (qw[C-local keys you want promoted]) {
my $temp = $ENV{$key}; # read from C-local array
$ENV{$key} = $temp; # and define as logical name
}
(You can't just say $ENV{$key} = $ENV{$key}, since the Perl optimizer is smart enough to elide the
expression.)
Don't try to clear %ENV by saying "%ENV = ();", it will throw a fatal error. This is equivalent to doing
the following from DCL:
DELETE/LOGICAL *
You can imagine how bad things would be if, for example, the SYS$MANAGER or SYS$SYSTEM logical names were
deleted.
At present, the first time you iterate over %ENV using "keys", or "values", you will incur a time penalty
as all logical names are read, in order to fully populate %ENV. Subsequent iterations will not reread
logical names, so they won't be as slow, but they also won't reflect any changes to logical name tables
caused by other programs.
$^E This variable provides direct access to VMS status values in vaxc$errno, which are often more specific
than the generic Unix-style error messages in $!. Its numeric value is the value of vaxc$errno, and its
string value is the corresponding VMS message string, as retrieved by sys$getmsg(). Setting $^E sets
vaxc$errno to the value specified.
While Perl attempts to keep the vaxc$errno value to be current, if errno is not EVMSERR, it may not be
from the current operation.
$? The "status value" returned in $? is synthesized from the actual exit status of the subprocess in a way
that approximates POSIX wait(5) semantics, in order to allow Perl programs to portably test for successful
completion of subprocesses. The low order 8 bits of $? are always 0 under VMS, since the termination
status of a process may or may not have been generated by an exception.
The next 8 bits contain the termination status of the program.
If the child process follows the convention of C programs compiled with the _POSIX_EXIT macro set, the
status value will contain the actual value of 0 to 255 returned by that program on a normal exit.
With the _POSIX_EXIT macro set, the Unix exit value of zero is represented as a VMS native status of 1,
and the Unix values from 2 to 255 are encoded by the equation:
VMS_status = 0x35a000 + (unix_value * 8) + 1.
And in the special case of Unix value 1 the encoding is:
VMS_status = 0x35a000 + 8 + 2 + 0x10000000.
For other termination statuses, the severity portion of the subprocess's exit status is used: if the
severity was success or informational, these bits are all 0; if the severity was warning, they contain a
value of 1; if the severity was error or fatal error, they contain the actual severity bits, which turns
out to be a value of 2 for error and 4 for severe_error. Fatal is another term for the severe_error
status.
As a result, $? will always be zero if the subprocess's exit status indicated successful completion, and
non-zero if a warning or error occurred or a program compliant with encoding _POSIX_EXIT values was run
and set a status.
How can you tell the difference between a non-zero status that is the result of a VMS native error status
or an encoded Unix status? You can not unless you look at the ${^CHILD_ERROR_NATIVE} value. The
${^CHILD_ERROR_NATIVE} value returns the actual VMS status value and check the severity bits. If the
severity bits are equal to 1, then if the numeric value for $? is between 2 and 255 or 0, then $?
accurately reflects a value passed back from a Unix application. If $? is 1, and the severity bits
indicate a VMS error (2), then $? is from a Unix application exit value.
In practice, Perl scripts that call programs that return _POSIX_EXIT type status values will be expecting
those values, and programs that call traditional VMS programs will either be expecting the previous
behavior or just checking for a non-zero status.
And success is always the value 0 in all behaviors.
When the actual VMS termination status of the child is an error, internally the $! value will be set to
the closest Unix errno value to that error so that Perl scripts that test for error messages will see the
expected Unix style error message instead of a VMS message.
of normal Unix parent or child status numbers, 0 to 255 are used.
The pragma "use vmsish 'status'" makes $? reflect the actual VMS exit status instead of the default
emulation of POSIX status described above. This pragma also disables the conversion of non-zero values to
SS$_ABORT when setting $? in an END block (but zero will still be converted to SS$_NORMAL).
Do not use the pragma "use vmsish 'status'" with "PERL_VMS_POSIX_EXIT" enabled, as they are at times
requesting conflicting actions and the consequence of ignoring this advice will be undefined to allow
future improvements in the POSIX exit handling.
In general, with "PERL_VMS_POSIX_EXIT" enabled, more detailed information will be available in the exit
status for DCL scripts or other native VMS tools, and will give the expected information for Posix
programs. It has not been made the default in order to preserve backward compatibility.
N.B. Setting "DECC$FILENAME_UNIX_REPORT" implicitly enables "PERL_VMS_POSIX_EXIT".
$| Setting $| for an I/O stream causes data to be flushed all the way to disk on each write (i.e. not just to
the underlying RMS buffers for a file). In other words, it's equivalent to calling fflush() and fsync()
from C.
Standard modules with VMS-specific differences
SDBM_File
SDBM_File works properly on VMS. It has, however, one minor difference. The database directory file created
has a .sdbm_dir extension rather than a .dir extension. .dir files are VMS filesystem directory files, and
using them for other purposes could cause unacceptable problems.
Revision date
Please see the git repository for revision history.
AUTHOR
Charles Bailey [email protected] Craig Berry [email protected] Dan Sugalski [email protected] John
Malmberg [email protected]
perl v5.16.3 2013-03-04 PERLVMS(1)
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